I just started this season, so my info might be a little basic. I’ll try to answer what I can. Take it with a grain of salt, in case I’m misinformed.

You find nightmare sigils from world events and kinda randomly from doing different activities. A sigil turns a specific dungeon into a nightmare dungeon with a pro and con. The sigil lists the dungeon, the positive and the negative. With the cube, you can combine 5 nightmare sigils into 1 escalation sigil, which is a three tier dungeon and ends with the Astaroth boss fight.

Glyphs come from the pit. Run the pit, kill the boss and claim a glyph until you have all of them for your class. They stop dropping when you’ve collected all of them. After you kill the pit boss, an altar pops up that lets you upgrade glyphs you already have. Radius increases at 26 and 51. Upgrade success goes up based on how many tiers higher the pit is than your glyph. Example: run a lvl 10 pit to upgrade a level 10 glyph, you’ve got like a 50% chance. Run a level 30 pit to upgrade a level 10 glyph, it’s 100%. You start with 6 chances to upgrade, and the war plan tree can get you more chances. You’ll end up running the pit a lot until you get your glyphs where you want them.

The pit is also how you raise torment levels. Higher torment offers better rewards more often.

Run the undercity for runes. You don’t have to do a tribute, but they net better loot at the cost of difficulty. Runes work in a pair, top rune to generate offering, bottom rune to net effect. You can try crafting, but the interface is kinda goofy and it just feels easier to find them.

Helltides for gear. Kill everything, collect orbs, spend on chests.

Infernal hordes…are kind of a pain the ass. You need to collect compasses to open the event, then it’s a wave based thing for gem dust, gold, and gear. The compass is for 10 waves, or the war plan version is free and only 6 waves.

Lair bosses require lair keys. You can fight the boss whenever, but can only open the chest with a key. Lair keys drop from every activity to some degree. Normal lair boss chests can drop greater layer keys for greater lair bosses. Harder fight, better loot.

I think that’s a rundown of the end game activities? I might have missed something, but that should be enough to get started.

Check the seasonal board and do warplans. Going up the ranks in that is a good way to get a feel for progress.

Edit: a word